In the mobile-phone system or wireless LAN (Local Area Network) comprised of base station apparatuses and terminal apparatuses, the terminal apparatus is generally powered by batteries. For the convenience when a terminal apparatus is used, the battery life of the terminal apparatus is desired to be longer. Accordingly, the lower power consumption is required for the processing executed by the terminal apparatus. In general, the terminal apparatus in the wireless communication system is not constantly transmitting and receiving the signals but is usually in an operational mode, namely, a receiving standby mode, in which the signal transmitted at predetermined time intervals from the base station apparatus are received when there is no data to be transmitted or received. In the receiving standby mode, it is not required that all of the receiving functions provided in the terminal apparatus is in operation. Accordingly, in the receiving standby mode, only part of receiving functions is working in the terminal apparatus to lower the power consumption (See Patent Reference (1) in the Patent Reference, for instance).
[Patent Reference]
(1) Japanese Patent Application Laid-Open No. Hei08-307428.
However, in order to further reduce the power consumption, the power consumed in transmitting or receiving the signals under other than the receiving standby mode must be reduced. For example, the wireless LAN complied with the IEEE 802.11b standard is compatible with a plurality of modulation schemes, namely, the modulation schemes whose transmission speed is high as well as those whose transmission speed is low. In general, the modulation scheme compatible with higher transmission rates is likely to be affected by the distortion in the propagation path and therefore the transmission quality of signals is likely to deteriorate. One of techniques to reduce the effect of distortion in such propagation path is the adaptive equalizer. However, the power consumption can be no longer reduced once the adaptive equalizer is in operation. On the other hand, although the adaptive equalizer is not in operation, the transmission quality of signals is unlikely to deteriorate in the modulation scheme compatible with lower transmission rates.